Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.26   12.327%   $119.3587   $119.36   $119.35   $119.40  
  Purchase #2 $181.68   12.489%   $204.37   $204.37   $204.35   $204.40  
  Purchase #3 $58.59   6.702%   $62.5167   $62.52   $62.50   $62.50  
  Purchase #4 $52.76   13.339%   $59.7977   $59.80   $59.80   $59.80  
  Purchase #5 $162.93   11.501%   $181.6686   $181.67   $181.65   $181.70  
  Purchase #6 $170.80   10.411%   $188.582   $188.58   $188.60   $188.60  
  Purchase #7 $6.34   10.630%   $7.0139   $7.01   $7.00   $7.00  
  7 purchase totals = $739.36       $823.3076   $823.31   $823.25   $823.40